1. Field of the Invention
The present invention relates to an image forming apparatus and a method for correcting a read signal.
2. Description of Related Art
Some image forming apparatuses read reference images in simple colors, mixed colors or such like formed on sheets of paper with reading sections and can calibrate the colors of images to be formed according to the obtained read signals. There are also image forming apparatuses which test the formed images by reading the images formed on the sheets and comparing the images with original images.
Read signals accurately indicating the colors of images on the sheets are necessary in order to perform accurate calibration and such like. However, when fluorescent whitening agent is used for the sheets in order to enhance the whiteness of the sheets, the colors reproduced by the read signals are not consistent with the colors observed by users in some cases.
In natural light, ultraviolet light included in the natural light is absorbed by the fluorescent whitening agent in a sheet, and light (fluorescence) is released. Since the fluorescence is visible light having a wavelength close to that of the ultraviolet light, the hue of blue color appears to be strong to the user and the whiteness of the sheet is enhanced. However, a reading section provided for calibration or the like generally uses a light source which emits visible light only. When only the visible light is emitted, fluorescence is not released from the fluorescent whitening agent. Since the read signal does not include the signal component of fluorescence, the color reproduced by the read signal has a less blue hue compared to the color observed by the user. Thus, the color reproduced by the read signal is not consistent with the color observed by the user.
Conventionally, whether or not the image color is a fluorescent color has been determined from the read signal value of the image, and if the image color is the fluorescent color, color correction for fluorescent color has been performed with respect to the signal value (for example, see Japanese Examined Patent Application Publication No. H6-83364).
However, though the fluorescent color can be determined from the read signal value of the image, it is not possible to determine how much the blue hue will be changed by the fluorescence. The color correction has been always performed with a same correction condition though the change amount of hue varies. Thus, the color after correction has not always been consistent with the color actually observed.